A gaslift system is one of the artificial lift techniques using worldwide for unloading and producing fluid from perforation intervals below the packer of the pay zones. Generally, a gaslift system utilizes lifting gas supplied from surface via a casing annulus for injecting into the tubing string via gaslift valves installed in the side pocket mandrels above the packer. The lifting gas is injected into the tubing string to decrease the hydrostatic pressure of the fluid column exerting on the perforation intervals or production zones below the packer. Therefore, petroleum fluids from the said perforation intervals can flow to the wellbore and up to the surface.
However, in many petroleum fields, it is desirable to produce two different formations comminglely or separately by using the same tubing string to provide savings in pipe and drilling costs. The producing formations are often at different pressures, and one may produce gas, the other oil. The two formations, under these conditions, must of necessity be produced separately. It is also desirable to obtain such production commingle multiple zones through the tubing and through the annulus space between the casing and the tubing.
There are several patents, which disclose system and apparatus for use in petroleum fluid production of multiple zone wells, such as:
U.S. Pat. No. 2,847,072 entitled “Methods for Dual Completion of Oil and Gas Wells” discloses a method for dual completion of wells. A production packer is set in the well casing between the formations to be produced and tubing is set in the well with the lower end thereof above the upper formation. The upper and lower formations are then respectively perforated, leaving the tubing end open. A tubing extension that passes through the production packer is connected to the tubing to establish communication between the lower formation and the tubing. The two formations are effectively separated by the production packer after the tubing extension has been passed therethrough. The lower formation is produced through the tubing extension and simultaneously the upper formation is produced separately through the space between the casing and the tubing.
U.S. Pat. No. 2,986,216 entitled “Apparatus for use in Wells Completed in a Plurality of Zones” discloses an apparatus comprising a tubing string arranged in a casing with its open lower end permanently placed above the upper of the zones. A mandrel is attached to and forms the lower end of the tubing. A first packer is arranged on the lower end of the mandrel closing off the casing-tubing annulus, and a second packer having an open bore is arranged below the lower end of the mandrel to separate the upper and lower zones. The upper portion of a tubular member forms a piston slidably mounted in the mandrel and its lower end is provided with seals for placement in the open bore of the second packer. By applying fluid pressure down the tubing to the piston, the tubular member is moved from a first position in the mandrel to a second extended position whereby its lower end is sealed in the open bore of the second packer. A first flow path is provided through the tubular member and tubing in the lower zone to the earth surface and a second flow path from the upper zone through a port in the mandrel or through a second tubing string having its lower end above the upper of the plurality of zones.
Those aforementioned prior arts rely on many devices and the systems thereof are rather complex. It is therefore difficult and expensive to service in case it is necessary to remove maintenance or adjust some devices of the well system.